diff --git a/src/services/note_cache/note_cache_service.js b/src/services/note_cache/note_cache_service.js
index 5eaa725b5..234d6ed17 100644
--- a/src/services/note_cache/note_cache_service.js
+++ b/src/services/note_cache/note_cache_service.js
@@ -152,6 +152,12 @@ function getSomePath(note, path = []) {
 
 function getNotePath(noteId) {
     const note = noteCache.notes[noteId];
+
+    if (!note) {
+        console.trace(`Cannot find note ${noteId} in cache.`);
+        return;
+    }
+
     const retPath = getSomePath(note);
 
     if (retPath) {
diff --git a/src/services/search/note_set.js b/src/services/search/note_set.js
index 3f8dc9dcf..626730d68 100644
--- a/src/services/search/note_set.js
+++ b/src/services/search/note_set.js
@@ -4,6 +4,7 @@ class NoteSet {
     constructor(notes = []) {
         /** @type {Note[]} */
         this.notes = notes;
+        this.noteIdSet = new Set(notes.map(note => note.noteId));
         /** @type {boolean} */
         this.sorted = false;
     }
@@ -11,6 +12,7 @@ class NoteSet {
     add(note) {
         if (!this.hasNote(note)) {
             this.notes.push(note);
+            this.noteIdSet.add(note.noteId);
         }
     }
 
@@ -25,12 +27,12 @@ class NoteSet {
     }
 
     hasNoteId(noteId) {
-        // TODO: optimize
-        return !!this.notes.find(note => note.noteId === noteId);
+        return this.noteIdSet.has(noteId);
     }
 
     mergeIn(anotherNoteSet) {
         this.notes = this.notes.concat(anotherNoteSet.notes);
+        this.noteIdSet = new Set(this.notes.map(note => note.noteId));
     }
 
     minus(anotherNoteSet) {